Natural bond orbital (NBO) population analysis of some benzyl nitrites

Theoretical study of several benzyl nitrites have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G∗∗ basis set. Geometries obtained from DFT calculations were used to perform NBO analysis. It is noted that weakness in the O3-N2 sigma bond is due to nO1→σO3-N2∗ delocalisation and is responsible for the longer O3-N2 bond lengths in the selected benzyl nitrites. It is also noted that decreased occupancy of the localized σO3-N2 orbital in the idealized Lewis structure, or increased occupancy of σO3-N2∗ of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of σO3-N2 bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of substituent groups.